Device for the transmission of torque

ABSTRACT

A device for transmitting a torque between two rotational elements (5, 2), includes an inner gear ring (24) that via only a few teeth engages an outer gear ring (23) being member of a cover (17) that is connected with one of the rotational elements (2). The axis of symmetry (A) of the gear ring (24) is oblique relative to the axis of symmetry (B) of the rotational elements (5, 2). By the aid of an eccentric portion (27) the gear ring disc (21) is imparted to perform a planetary motion along the outer gear ring (23), whereby a transmission element, that supports the inner gear ring, is subjected to a nutating motion. Between a stationary member (12) and the gear ring disc (21) a bellows (13) is provided, said bellows (13), in a hermetically tight way, separating the spaces (14,15) where the rotational elements (5, 2) are located.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a device for transmitting a torque between afirst driving or driven rotational element, said element being locatedin a first space and rotatable relative to a first stationary member,and a second driving or driven rotational element, said element beinglocated in a second space and rotatable relative to a second stationarymember, more precisely by means of a transmission element operatingbetween said elements, said first and second spaces being separated fromeach other via a tight separating means.

BACKGROUND OF THE INVENTION AND PRIOR ART

The grounds for this invention are the sealing problems that relate tovalve spindles. Rotatable as well as axially movable valve spindles arein practice often sealed by gland or radial sealings. These sealingsinclude a set of rings that via a washer and a number of screws arecompressed axially in order to expand radially and thus create a sealingbetween the spindle and a surrounding valve housing. However, thesealing is worn and consequently the sealing pressure decreaseseventually. A regular follow-up draft of the screws is thus required.Sometimes spring washers beneath the heads of the screws are used togive a more long-lasting axial prestressing of the set of rings. Forcertain types of valves O-ring sealings are also used. These sealingshave the disadvantage that the valve must be dismounted when the O-ringis to be exchanged.

Common for prior art valve sealings is that a relative movement takesplace in the interface between the sealing material and the spindle.This means that the sealing will never become hermetically tight inabsolute terms and as soon as the sealing is worn its sealing ability isreduced gradually. In e.g. the process industry, like chemical industry,there are very high demands upon valve tightness since fluids, whoseflows are regulated by means of a valve, may be toxic as well ascorrosive. A leaking gas valve, e.g. at an oil rig, may causecatastrophes.

Hermetically tight valves that use metal bellows are known for suchvalves where the valve operation is effected by an axial movement only,e.g. sliding valves and seat valves. In such a case the valve spindle atits outer end is provided with a thread that cooperates with ajournalled nut that upon rotation causes the spindle to move axially.Inside of the thread and the nut a metal bellows is provided and it ispossible to secure said metal bellows both to the spindle and thesurrounding valve housing in a hermetically tight way due to the factthat the spindle moves only axially, i.e. without rotating. For othertypes of valves, e.g. ball valves, cap valves and revolving butterflyvalves, it is necessary when operating said valves that the spindle isrotated or turned. This makes it impossible to secure a bellowshermetically tight to the spindle. The operation of said valves oftenrequires that high torques are transmitted from the driving source inquestion to the rotatable spindle and the adherent valve body.

From a narrow aspect the aim of the invention is to realize a devicethat manages to transmit also high torques to a rotatable valve spindlesimultaneously as the spindle is kept separated from the surroundings bymeans of a separating means that is hermetically tight. From a mostgeneral aspect the aim of the invention is to create a device fortransmitting a torque that could be used wherever a rotational elementis to transmit a torque to another rotational element simultaneously asthe elements are kept apart by means of a hermetically tight separatingmeans.

A device as generally defined in the preamble for transmitting a rotarymotion is previously known for other purposes than operation of valvespindles. This known device has two rotational elements that consist ofinput and output shafts that are rotatably journalled in opposite wallsof a housing that is placed in a partition between two separated spaces.The transmission element consists of a rigid arm that is pivotallyjournalled by means of a ball and socket joint located between the endsof the arm, the opposite ends of the arm being hingedly connected withdiscs on the input and output shafts respectively; more precisely insuch a way that the arm transmits a rotary motion with a gear change of1:1 from the input shaft to the output shaft. The arm is provided with aplate to which an end of a conically shaped bellows is tightly secured,the opposite end of the bellows also being tightly secured to one ofsaid walls in the housing.

For several reasons it is not in practice possible to use a device ofthe last-mentioned type for transmitting high torques between input andoutput rotational elements, e.g. in a valve, simultaneously ashermetical sealing is guaranteed. Thus the bellows is moving with largestrokes; this means that the bellows must not be made out of materials,e.g. metallic materials, that are resistant to high pressures. Furtherthe arm that takes care of the transmission of rotation of the inputshaft to the output shaft has such weak dimensions that it is not at allpossible to transmit higher torques. Still further the structure doesnot allow fine adjustment of the output rotational element in differentsetting positions.

OBJECTS AND FEATURES OF THE INVENTION

As mentioned above, in its most general aspect the invention aims atcreating a device for transmitting a torque that manages to transmitconsiderable torques between two rotational elements, one of which isdriving and the other one is driven, simultaneously as these elementsare to be located in spaces that are separated from each other by meansof hermetically tight separating means. A further aim is to create sucha device that manages to resist considerable compressive forces withoutdemolition or damage of the separating means. Still an aim is to createa torque transmitting and simultaneously hermetically sealing devicethat manages to resist the influence of even extremely aggressive and/ortoxic fluids without demanding a complicated or expensive design. It isalso an aim to create a device that claims only a minimal room, e.g. inconnection with a valve spindle.

According to the invention at least the basic aim is realized by thecharacteristics defined in the characterizing clause of claim 1.Preferred embodiments of the invention are defined in the dependentclaims.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

In the drawings:

FIG. 1 is an illustration, partly in view, partly in section of a valvedesign that includes a device according to the invention fortransmitting a torque,

FIG. 2 is an enlarged, schemetical longitudinal section through thedevice according to the invention only, said device being shown inhorizontal position,

FIG. 3 is a transverse section III--III in FIG. 2,

FIG. 4 is a schematical longitudinal section showing an alternativeembodiment of the invention.

FIG. 5 is an analog longitudinal section showing a third embodiment, and

FIG. 6 is a longitudinal section showing a fourth embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1 the reference numeral 1 generally designates a valve housingincluding a valve means (not shown), e.g. a ball, a revolving throttleor the like, said valve means for regulating purposes, being connectedwith a spindle or a shaft 2. In order to bring the shaft 2 to rotatethere is a driving element that according to the example is in the shapeof a wheel 3 having a handle 4. An input shaft 5 is connected with thewheel 3, said input shaft 5 being lockable by means of a locking element6. A device according to the invention is inserted between the inputshaft 5 and the shaft 2, said device as a whole being given thereference numeral 7. The device is incorporated in a housing 8 thatincludes on one hand a tubular wall 9 that is secured to a flange 10 bymeans of bolts 11 and on the other hand an end wall 12. The deviceaccording to the invention also includes a bellows being designated 13,said bellows 13 separating two different spaces inside the housing 8,i.e. a first space 14 in connection with the input shaft 5 and a secondspace 15 in connection with the valve spindle 2.

It should also be mentioned that the valve spindle 2 is surrounded by aconventional radial sealing 16.

Reference is now made to FIGS. 2 and 3 that schematically illustrate afirst embodiment of the invention. In FIG. 2 the device according to theinvention is shown in a horizontal position where the end wall 12 islocated to the left and forms a first stationary member, the shaft 5being rotatable relative to said stationary member. Compared to theinput, driving shaft 5 the valve spindle 2 is an output, driven shaft.It should be noted that said shaft 2 at its end is connected to a coverthat in its entirety is designated 17, said cover being composed of adisc shaped wall 18 and an annular or tubular flange 19. The two spacesthat are separated by means of the bellows 13 are shown at 14 and 15respectively.

The main component of the device according to the invention is atransmission element that is generally designated 20. In the givenexample said transmission element 20 is composed on one hand of a disc21 and on the other hand of a sleeve or sleeve-shaped member 22 thatprojects from said disc 21. A first outer gear ring 23 on the inside ofthe annular flange 19 is arranged to cooperate with a second, inner gearring 24 on the periphery of the circular disc 21. Said two gear rings23, 24 have different pitch diameters. The outer gear ring 23 has acertain number of inwardly directed teeth, while the inner gear ring 24has a smaller number of outwardly directed teeth of which only a minornumber, e.g. one, is in engagement with the outer gear ring 23. Saidouter gear ring 23 is cylindrical in the given example (but could alsobe conical). The inner gear ring 24 is preferably conical. An axis ofsymmetry of the gear ring 24 is designated A. Said geometrical axis ofsymmetry is oblique at an angle A relative to the axis of symmetry B ofthe driving shaft 5.

From the inside of the end wall 12 a tube socket 25 extends, saiddriving shaft 5 being journalled, by the aid of a proper number ofschematically disclosed bearings 26, 26', relative to the tube socket25. At its inner end the driving shaft 5 has an eccentrically locatedportion 27 that engages a centric recess 28 in the gear disc 21. Saideccentrical portion 27 is preferably in the shape of a cylindricalspigot having its centre axis coaxially with the axis of symmetry A. Thedisc 21 is journalled relative to the eccentrical spigot 27 by means ofa schematically disclosed bearing 29. The angle μ between the axes ofsymmetry A and B is in practice very small, e.g. in the interval0,4-1,0°. Depending on the length of the sleeve 22 the eccentricity "ee"of the spigot 27, relative to the axis of symmetry B, could be in themagnitude of 0,3-0,6 mm. Thus in FIG. 2 the angle μ is shown too largefor better clarity.

At its end directed away from the disc 21 the sleeve 22 is connectedwith the stationary member 12 by means of a coupling 30 that guaranteesa non-rotative connection between said stationary member 12 and thetransmission element 20 as a whole simultaneously as said connectionallows the element 20 to perform a slewing or nutating motion. Thecoupling 30 is located in a plane C that extends perpendicular to theaxis of symmetry B, said plane C intersecting said axis of symmetry B ina point D where also the axis of symmetry A intersects the axis ofsymmetry B. In practice the coupling 30 could be in the shape of a gearcoupling or a ball spline coupling of the type described in SE9404154-8.

Generally the bellows 13 forms a tubular or, in cross-section, annularseparating means having its two opposite ends 13' and 13" respectivelytightly secured to the element 20 and the stationary member 12respectively. More precisely the end 13' is secured to the portion ofthe sleeve 22 that is closest to the disc 21 while the end 13" issecured to an annular flange 31 that partly defines an annular groove 32in the end wall 12. Said groove 32 has a planar bottom 33, said sleeve22 contacting said planar bottom 33, more precisely the contact isessentially in the shape of linear contact (in order to guarantee linearcontact the end of the sleeve could be slightly conical). The attachmentof the two ends of the bellows 13 against the sleeve 22 and the theannular flange 31 respectively is carried out in such a way that thebellows seals hermetically. In practice the bellows could be made out ofmetal, e.g. stainless steel, and the securing is effected by means ofwelding, brazing, deep rolling, gluing or the like.

The Function of the Device according to the Invention

When the driving shaft 5 is brought to rotate the eccentric spigot 27and thus also the gear disc 21 will perform a planetary or arc-shapedmotion around the central axis of symmetry B. This results in that thetooth or the few teeth of the inner gear ring 24 that engage the outergear ring 23 will generate on the outer gear ring 23, the element 20 asa whole performing a nutating motion and the axis of symmetry A duringsaid motion moving as a generatrix along an envelope surface of animaginary cone, more precisely around the point D that forms a cone apexthat is axially separated from the gear rings. During this nutatingmotion the transmission element 20 and its gear disc 21 does not rotatesince the element 20 being non-rotatively connected to the stationarymember 12 via the coupling 30. However, the result of the motion is thatthe cover 17 and also the shaft 2 are brought to rotate, more preciselyin the same direction of rotation as the driving shaft and by a gearchange that is dependent from the the difference between the number ofteeth of the respective gear rings. If it is assumed that the number ofteeth in the outer gear ring 23 is 101 and the number of teeth in theinner gear ring 24 is 100 then the gear change is 100:1, i.e. the shaft2 moves 1/100 revolution when the driving shaft 5 is rotated onerevolution. The consequence of this large gear change is that very hightorques can be transmitted from the shaft or valve spindle 2.

The benefits of the invention are several. Due to the small eccentricityof the gear disc 21 the bellows 13 will be subjected to very smalldeformations and thus if needed the bellows could be designed with arelatively substantial wall thickness, e.g. out of acidproof steel, andthere is no risk that the tension in any member of the bellows reachesthe fatigue limit. Thanks to the diminutive nutating motions of the geardisc it is possible to design the hermetically tight joints or seams atthe ends 13', 13" of the bellows in a very reliable way and with asubstantial length of life, said joints or seams being connected withthe sleeve portion 22 and the gear ring 31 respectively. At the sametime as the device according to the invention, by means of the bellows13, is able to seal the two spaces 14 and 15 from each other in a veryreliable way it is also guaranteed that high torques can be transmittedfrom the driving shaft to the valve spindle. If the disc 21 is subjectedto a high pressure from a fluid in the space 15, said pressure iscarried by the sleeve 22 without any axial compression of the bellows13. Thus the free end of the sleeve 22 rests against the bottom 33 ofthe groove 32 and more precisely along a contact line that moves aroundthe annular bottom surface syncronized with the nutating motion of thesleeve. This means that the bearings 26, 26' and 29 need to carry radialload only and no axial load.

In FIG. 4 an alternative embodiment is shown where the coupling 30according to FIG. 2 is omitted and replaced by a ball joint structureincluding a partly spherical bulge 35 having its centre located in thecone apex D. At its free end the sleeve 22 has an internal, cylindricalsurface 36 that with fairly tight fit contacts the partly sphericalsurface of the bulge 35. This ball joint allows the sleeve and theadherent gear disc 21 to perform the nutating motion described above.Non-rotative connection between the stationary member 12 and the geardisc 21 is in this case guaranteed by means of the bellows 13 itselfthat thanks to the tubular shape has a substantial torsional stiffness,the bellows 13 at its opposite ends being fixedly connected with theannular flange 31 and the sleeve 22 respectively.

In the embodiment according to FIG. 5 the transmission element 20consists essentially of the gear disc 21 only, i.e. apart from anannular projection 37 there is no sleeve of the kind shown in FIGS. 2and 4. The diminutive projection 37 serves as holder for the bellows 13.In this case the axial compressive forces that possibly act upon thegear disc 21 are carried by two bearings 38, 39, an additional object ofsaid bearings 38, 39 being to journal the driving shaft 5 relative tothe tubular portion 25 and the gear disc 21 relative to the eccentricspigot 27.

In theory it would be possible, instead of a conical inner gear ringhaving oblique axis of symmetry, to use a cylindrical inner gear ringthat is eccentrically movable relative to the input shaft in a planeperpendicular to said shaft. In such a case the bellows would beimparted a S-shape during the eccentric movements of the gear disc. Thebellows according to the invention has a simple arched shape when thegear disc with its conical gear ring performs its nutating motion. Inpractice this means among other things that for equal deformation stressupon the bellows a double torsional stiffness is achieved since thebellows will have only half the length compared to the S-shaped designand the overall structural length is thus shorter.

To maintain the conventional radial sealing 16 in connection with thevalve spindle 2, as is shown in FIG. 1, is of advantage in that anysudden pressure changes may not occur in the space 15 between thesealing and the bellows. If in an extreme situation a crack would occur,in e.g. a welding in connection with the bellows, the radial sealingguarantees that large quantities of the fluid in question will not flowout in a forced flow. In other words the radial sealing guarantees thatthe quantity of possibly leaking fluid that by-passes a demolatedbellows is small per time-unit.

As shown in FIG. 2 it is also possible that the device is completed withat least one further sealing 40, e.g. an O-ring. The pressure in thespace between the bellows and the O-ring can be detected in a suitableway, e.g. by means of a pressure transmitter that gives warning if thereis a pressure increase, i.e. the bellows is leaking.

In FIG. 1 it is further shown how a collar bearing 41 could be arrangedon the outside of the annular flange 19 of the cover 17. In practicesaid bearing could be in the shape of a needle roller bearing thatunrolls directly against the outside of the annular flange 19 andagainst a strip of hardened steel that is located in a turned groove inthe tubular wall 9 of the surrounding housing 8.

According to the embodiment of FIG. 6 the separating means 13 consistsof an annular, membrane-like disc that has its outer periphery securedto the stationary member 12 and its inner periphery to a flange 42 ofthe sleeve 22. In the area between its outer and inner edges the annulardisc 13 has corrugations 43 that make the nutating motion of thetransmission element possible.

Feasible Modifications of the Invention

The invention is not restricted only to the embodiments described andshown in the drawings. Thus it is possible to adapt the general scope ofinvention also for other applications than valve control. It is thusonly essential for the invention that a torque is transmitted betweentwo rotational elements simultaneously as the spaces holding theserotational elements are hermetically sealed or separated from eachother. In this connection it should be emphazised that the forcetransmission could take place in reverse direction, i.e. the first shaft5 could be an output shaft, while the second shaft 2 constitutes aninput shaft. Further it is obvious that the input shaft could be drivenin a different way than by a manually actuated driving means, e.g. anelectric or other motor. It is neither necessary to use exactly abellows as a barrier or separating means between the two spaces that areto be separated. Through suitable choice of material it is thus alsopossible to use a simple tube or even a simple annular disc of the typeshown in FIG. 6. It should also be pointed out that the two gear rings23, 24 preferably could have a helical line contact between the teeth ina way described in WO 95/07420. Also the input shaft 5 could be designedin a suitable way having a counterweight to balance the eccentricportion 27 and a part of the total nutating mass.

I claim:
 1. A torque transmitting device, comprising, a rotational shaft(5) located in a first space (14) and rotatable relative to a stationaryfirst member (12), and a rotational element (2) located in a secondspace (15) and rotatable relative to a stationary second member (1), atransmission element (20) operatively connected between said shaft andsaid rotational element and structured and arranged to impart rotationof one of said shaft and rotational element by rotation of the other ofsaid shaft and rotational element, said transmission element (20) beingnon-rotatively connected with said first member 12 and comprising a dischaving a centric recess, a separating member (13) connected to saidfirst member (12) and said transmission element (20), said separatingmember (13) separating said first and second spaces, cooperating firstand second gear rings (23,24) having different pitch diameters, saidfirst gear ring being an outer gear ring (23) coupled to said rotationalelement, said outer gear ring comprising inwardly directed first teeth,and said second gear ring being an inner gear ring at an outerperipheral edge of said disc, said inner gear ring comprising outwardlydirected second teeth, the diameter of said outer gear ring (23) beinggreater than the diameter of said inner gear ring (24), the number ofsaid first teeth being greater than the number of said second teeth, andonly a minor number of said second teeth being in engagement with saidfirst teeth in an operative mode, said inner gear ring (24) having afirst geometric axis of symmetry (A), and said outer gear ring (23),said shaft (5) and said rotational element (2) having a second geometricaxis of symmetry (B), said first geometric axis of symmetry (A) beingoblique relative to said second geometric axis of symmetry (B), one endof said shaft (5) comprising a portion (27) in engagement with saidcentric recess (28), said portion (27) being eccentric relative to saidsecond geometric axis of symmetry (B), wherein in said operative mode,said inner gear ring (24) is eccentrically movable relative to saidouter gear ring (23), and said first axis (A) has a nutating andgeneratrix motion along an imaginary envelope surface of a cone andaround an apex (D) of said cone, said apex being axially separated fromsaid outer and inner gear rings.
 2. Device according to claim 1, whereinsaid portion (27) comprises a spigot (27) having a geometric centre axisco-axial with the first geometric axis of symmetry (A).
 3. Deviceaccording to claim 1, further comprising a sleeve-shaped portion (22)extending from said disc to a free end, and further wherein said freeend contacts the first member (12) thereby carrying axial compressiveforces acting against the disc and preventing said forces from actingupon the separating member (13), in said operative mode.
 4. Deviceaccording to claim 3, wherein the sleeve-shaped portion (22), at saidfree end, is connected with the first member (12) by a coupling (30)that is located essentially in the same transverse plane (C) as saidcone apex (D), that said coupling guarantees the non-rotative connectionbetween the first stationary member (12) and the inner gear ring (24)simultaneously as it is possible for the transmission element (20) toperform the nutating motion.
 5. Device according to claim 1 furthercomprising a first bearing (38) that journals the shaft (5) relative tothe first member, and a second bearing (39) that journals the disc (21)relative to the portion (27),, said first and second bearings comprisingroller bearings structured and arranged to carry radial and axial loads.6. Device according to claim 2 further comprising a sleeve-shapedportion (22) extending from said disc to a free end, and further whereinsaid free end contacts the first member (12) thereby carrying axialcompressive forces acting against the disc and preventing said forcesfrom acting upon the separating member (13), in said operative mode. 7.Device according to claim 1 wherein said separating member comprises atube having a substantial axial extension.
 8. Device according to claim2, wherein said separating member comprises a tube having a substantialaxial extension.
 9. Device according to claim 3, wherein said separatingmember comprises a tube having a substantial axial extension.
 10. Deviceaccording to claim 4, wherein said separating member comprises a tubehaving a substantial axial extension.
 11. Device according to claim 6,wherein said separating member comprises a tube having a substantialaxial extension.
 12. Device according to claim 2 further comprising afirst bearing (38) that journals the shaft (5) relative to the firstmember, and a second bearing (30) that journals the disc (21) relativeto the portion (27),, said first and second bearings comprising rollerbearings structured and arranged to carry radial and axial loads.